I went to Nepal for the first time in my early twenties and fell in love with the country. I knew I would be back. I had a seed in the back of my mind that I would like to walk from one end of the Himalayas to the other, but I didn't know whether it could be done.

Many years later I was at a point where my business life had become very stressful: I was running six car dealerships in Epsom, Surrey, employing 240 people. I promised myself that when I was 50 I would take time out and do something just for me. When a friend told me that the first commercial trek along the length of Nepal's Himalayas was taking place in 2011, I gave up work and booked a place.

I was one of only two people to sign up for the whole five-month, 1,700km trek, featuring 30 high-altitude mountain passes. The Nepal leg is the first completed section of the Great Himalaya Trail (GHT), which will eventually stretch 4,500km from Pakistan to Tibet.

I completed the Annapurna Circuit, a much shorter Nepalese trek, a couple of years ago, but I'd never done any proper climbing before this trip. I spent three months training on my local hill, Box Hill, which is only around 200m high. I would go up and down, up and down. Once I could manage that, I filled a rucksack with more and more two-litre water bottles until I was carrying 15kg.

We set off in February. On our way to Kangchenjunga base camp, everything was fresh and new and exciting. We were surrounded by stunningly beautiful mountains, and there was a lot of snow – much more than there would normally be at that time of year.

It was very, very cold. I had a down sleeping bag, an outer sleeping bag and an inner fleece liner – as well as a pink hot water bottle! When you're cold and doing a great deal of physical activity (on our longest days we walked for 10 hours) you burn a lot of calories, so I would eat three plates of everything. I would have three bowls of soup followed by three carbohydrate-heavy main meals – rice, potatoes, bread – to give me energy.

One day, when we stopped for lunch, we saw lots of fresh snow leopard prints all around us. When we went down to the river to fetch water, we found a dead Himalayan blue sheep with its hind legs ripped off. Looking up, we saw a snow leopard above us on the other side of the river, moving very slowly because of its full belly. It was six feet long, with a tail as long again, and much darker than I had expected. Its black spots and ash-coloured fur camouflaged it against the rocks.

I didn't feel frightened. I just felt amazed that I was lucky enough to see such a beautiful, extremely rare creature. Sadly it all happened too fast to take a photograph; by the time we'd got our cameras out the leopard had run off towards a nearby glacier.

Toni Wilson with a sherpa woman in Solukhumbu

I thought that anything would be an anti-climax after that – but it wasn't. Each day we were inspired by another beautiful landscape or welcomed into a local person's home, be it a yak herder's hut or the sherpa community up in Solukhumbu. We would sit around the fire drinking tongba (homebrew made from millet) and eating champa (a kind of porridge).

Stephen Venables, the first British mountaineer to climb Everest without oxygen, took us down the Sherpani Col, West Col and Amphu Labsta, three passes that are around 6,000m or above. The West Col has a 300m drop down a blue ice wall into a crevasse. That was pretty challenging.

I'm the first woman to complete the entire Nepal section of the GHT, and I've got the bug now. It won't be long before I'm back on the trail.

• World Expeditions (0800 074 4135, worldexpeditions.co.uk) is running the next Nepal GHT trek from 14 February to 19 July 2012; choose from one of the seven stages or the full traverse (which costs £19,990pp)